Multirange superheterodyne receiver



km 1934 P. o. FARNHAM MULTIRANGE SUPERHETERODYNE RECEIVER Filed Dec. 28, 1931" Patented Jan. 16, 1934 UNITED STATES PATENT OFFICE MULTIRANGE SUPERHETERODYNE RECEIVER Application December 28, 1931 Serial No. 583,488

12 Claims.

This invention relates to superheterodyne receivers and more particularly to receivers adapted to be operated over a plurality of frequency bands.

It has been Considered impractical to operate superheterodyne radio receivers over a plurality of frequency bands as an intermediate frequency which is best adapted for one frequency band will not be satisfactory for reception at another frequency band. I have discovered that reception over a plurality of frequency bands may be made perfectly practical by suitable adjustment of the intermediate frequency for each frequency band. For any one frequency range, the

practice has been to select that intermediate fre quency which represents the best compromise between image frequency interference and disturbance from intermediate frequency harmonies.

According to the present invention, this design requirement is satisfied by changing not only the carrier and oscillator tuning ranges but also the intermediate frequency when shifting from one band to another.

An object of the invention is to provide a superheterodyne receiver for operation over a plurality of, frequency bands, and one which is tuned to a different intermediate frequency for each frequency band. A further object is to provide a superheterodyne receiver capable of operation, by manipulation of a simple switch arrangement, over a plurality of frequency bands. More particularly, an object is to provide a superheterodyne receiver for operation over a plurality of frequency bands by the use of interchangeable inductances or switches for adjusting the effective values of the inductances in the carrier wave, oscillator and intermediate frequency stages; the values of the several inductances for the different frequency bands being so related that no adjustment of capacitive reactances is required to provide proper tracking of the oscillator over all frequency bands.

These and other objects. as well as the advantages of the invention, will be apparent from the following specification, when taken with the accompanying drawing in which the single view is a fragmentary circuit diagram of a superheterodyne receiver embodying the invention.

In the drawing, the reference numeral 1 identifies a carrier wave amplifier tube which receives signal energy from a collector structure 2 of any desired form. The amplified signal energy from ube 1 is transmitted to a first detector tube 3 where it beats with locally generated oscillations from the oscillator tube 4 to produce a modulated signal of intermediate frequency which is impressed upon an intermediate frequency amplifier tube 5. This will be recognized as a conventional arrangement of coupled tube circuits in a superheterodyne receiver and one which may be varied, in accordance with the particular design requirements, by the introduction of additional carrier wave and/or intermediate frequency amplifier stages. The present invention does not relate to the general arrangement of the several tube circuits in a superheterodyne receiver, but to the particular circuits, constructions of the several stages and their relationships to each other.

In accordance with the present invention, the several tube circuits of a superheterodyne receiver are so constructed and arranged that, without change in the capacitive reactances of the several stages, the several tuned circuits will track properly over a plurality of frequency hands by appropriate choice of the inductances employed in the several types of tube stages,

i. e., the carrier and intermediate frequency amplifiers and the oscillator. The magnitudes of the inductances included in the resonant circuits of these several types of stages may be varied by the use of interchangeable coils or by tapped coils and switches. For purposes of illustration, tapped coils and switches are shown and, for this particular type of adjustable inductance, the coils preferably take the form described and claimed in the copending application of W. D. Loughlin and Paul O. Farnham, Ser. No. 563,180, filed September 16, 1931.

The input circuit of the carrier wave amplifier tube 1 is shown as including a tapped inductance L shunted by a tuning condenser C, the switch for varying the effective inductance of coil L ineluding a contact arm 6 for progressively grounding and short circuiting sections of coil L as the switch is manipulated to adapt the receiver for the reception of signals in progressively higher frequency bands, as explained in detail in the aforesaid copending application. The coupling between the first detector tube 3 and the preceding carrier wave amplifier stage may take the form of a transformer having a secondary L substantially identical with the described tapped inductance L and switch arm 6, 1 5 the primary winding Ll of the transformer being wound turn for turn with the inductance L and included. as is customary. in the plate circuit of the lastcarrier wave amplifier stage.

The Coupling b tv rvn th first detector 3 and 11 the first intermediate frequency amplifier 5 may be of the auto-transformer or tuned impedance type and is illustrated as including a tapped inductance L2 in the plate circuit of the detector; a switch arm 7 being provided for adjusting the effective impedance of the inductance L2 that is shunted by the trimming condenser 8. As indicated by the broken lines 9 connecting the several switch arms 6 and switch arm 7, the switch rms are preferably connected mechanically for simultaneous adjustment.

With tuned carrier wave and intermediate frequency circuits of the described types, it will be apparent that the oscillator t must be operated over different frequency bands in accordance with the particular frequency band in which the desired signal frequency is to be found. As illustrated, the circuit network of the oscillator tube 4 includes a plate inductance or primary coil L3, a coupling condenser 10 between the plate and control grid, and a tuned secondary Li. A capacity l2, shunted by a resistor 13, is connected between the control grid and cathode of the oscillator tube 4. The direct current potentials applied to the tube elements are so related that the tube 4 operates as a dynatron oscillator, supplemented by feed back from the plate to the control grid, thus insuring oscillation at the higher frequencies.

The tuning condenser C of the oscillator is preferably substantially identical with the tuning condensers of the carrier wave and detector stages, as is indicated by the broken line which indicates that these tuning condensers are mechanically connected for simultaneous operation. The oscillator tuning condenser C is not connected directly across the plate inductance La but is connected across the secondary winding L4 of a transformer which has the plate induc tance L: as the primary winding thereof. The high potential terminals of the transformer windings are connected by a condenser C2, and the windings are twin windings constituting a transformer similar to the transformer coupling the detector to the preceding carrier wave amplifier stage.

The maximum value of L4 is somewhat less than that of the maximum value of the carrier wave inductances L and, to secure alinement of the oscillator with the carrier wave circuits,

' the oscillatory circuit of tube 4 includes, in addition to inductance L4 and adjustable condenser C, the relatively fixed series lagging condenser 15 and the bottom capacity or condenser 16 shunted across the oscillator tuning condenser C.

The inductance L4 of the oscillator circuit is tapped and a switch arm 17 is provided for adjusting the effective value of this inductance, and thereby of the twin winding L3. The switch arm 17 is mechanically connected, as indicated by broken line 18, to the switch operating mechanism 9 of the switch arms of the carrier and intermediate frequency stages.

In accordance with the well known method of tracking the oscillator and carrier circuit frequencies to provide a substantially constant difference or intermediate frequency with singlecontrol operation over any one frequency band covered by the capacities C, the oscillator circuit includes a series lagging condenser 15, and additional shunt condenser 16.

Mathematical considerations will show that in a system of carrierand oscillator circuits whose inductances are given different effective values for the purpose of covering different frequency bands, the resulting intermediate frequencies will, in general, be different for each band.

In accordance with this invention, the inter" mediate frequency for each carrier frequency band is related to the minimum carrier frequency of that band by a factor which is the same for all bands. This relation provides the optimum intermediate frequency for each band with regard to the necessary compromise between image frequency interference, feed back effects due to harmonics of the intermediate frequency, and selectivity. In the construction of a multirange superheterodyne receiver, this desirable relation is most readily obtained by so relating the several inductive reactances of the oscillator circuit to the corresponding inductive reactances of the carrier circuit that no readjustment of the capacitive reactances in the oscillator circuit is required for maintaining the desirable relation between intermediate and carrier frequencies. as described above, in going from band to band.

According to this invention, no readjustment of the alining capacities in the oscillator circuit is required in going from band to band if the effective oscillator inductance bears a constant ratio to the effective carrier inductance for all bands.

The following data is illustrative of the values employed in one practical embodiment of the invention which was designed for reception of signals within five bands that extended from 500 to 16,000 kilocycles.

Minimum Inler- Effective Band carrier mediate frequency frequency L Kilocycles O0 150 0. 300 O. 75 600 O. 75 1,200 0. 75 2, 400 0. 75

and frequencies, the value of the series lagging capacity 15 was 3.3 times the maximum capacity of the oscillator tuning condenser C, and was of constant value for all frequency bands.

It is to be understood, however, that the invention is not limited to this particular relationship of the several resonant circuits or to the particular circuit arrangements herein illustrated. Other types of oscillators may be employed and the magnitudes of the intermediate frequencies for the several stages may be varied within known limits as established by known design practice.

I claim:

1. In the operation of a superheterodyne receiver having a carrier frequency input circuit and an oscillator each adapted to b tuned over a plurality of frequency bands, the method of re ceiving signals in different frequency bands which comprises providing a different but constant intermediate frequency for each band of received signal frequencies. and employing with each band of progressively higher frequency range a progressively higher intermediate frequency.

2. In the operation of a superheterodyne receiver having a carrier frequency input qircuit and an oscillator each adapted to be tuned over a plurality of frequency bands, the method of maintaining a desired selectivity over the several frequency bands which comprises providing a constant but different intermediate frequency for each of said frequency bands, and employing with each band of progressively higher frequency range a progressively higher intermediate frequency.

3. In the operation of a superheterodyne receiver having a tuned carrier frequency circuit and a tuned oscillator circuit, the method of receiving signals in different frequency bands which comprises employing a different intermediate frequency for each band of received signals. and adjusting the respective effective inductances of the carrier frequency circuit and the oscillator circuit to a fixed but different value for each frequency band while maintaining a constant ratio between said effective inductances throughout the entire tuning range, whereby beat frequencies of constant but different magnitudes may be produced for each band of carrier frequencies when only the effective inductances of said circuits are so adjusted to their several different values.

4. A superheterodyne receiver for operation over a plurality of frequency bands, and of the type including a resonant carrier wave circuit and a resonant oscillator circuit each having a relatively fixed inductance and tuned by similar sections of a gang condenser, characterized by the fact that the relatively fixed inductances of said circuits are tapped to permit reception of signals in the different frequency bands, and the sections of said tapped inductances are so related that the effective inductances of said circuits have a constant ratio for all frequency bands.

5. In a superheterodyne receiver having oscillator and carrier frequency stages simultaneously tuned by substantially identical units of a gang condenser, the combination with carrier frequency stages having resonant input circuits including inductances of different magnitudes, of an oscillator having an oscillatory circuit including an inductance of variable magnitude, the several effective magnitudes of said inductances being so related that the ratio of the magnitude of the inductance effectively -included in said carrier frequency stages to the magnitude of the inductance of said oscillatory circuit is a constant for all frequency bands of received signal energy.

6. In a superheterodyne receiver adapted for the reception of signals within a plurality of frequency bands, the combination with a carrier wave amplifier, a tuned oscillator, and means for adjusting the amplifier for the reception of signals within a. given frequency band, of means for adjusting the tuning range of said oscillator to produce beat frequency signals with the desired signalof a constant but different frequency for each of said carrier wave frequency bands.

7. In a superheterodyne receiver, the combination with a carrier frequency amplifier, an oscillator stage, and means for adjusting said amplifier for the reception of signals within the desired one of a plurality of frequency bands, of means operable simultaneously with said first mentioned means for adjusting said oscillator to produce oscillatory currents for combining with the signal of desired frequency to produce an intermediate frequency signal of constant but different frequency for each of said signal frequency bands.

8. In a superheterodyne receiver, the combination with a carrier wave amplifier, and an intermediate frequency amplifier, an oscillator, of means for tuning the carrier wave amplifier over a plurality of frequency bands, means for adjusting said intermediate frequency amplifier to a constant but different frequency for each of said carrier frequency bands and means for adjusting said oscillator for tuning over a different frequency band for each of said carrier frequency bands.

9. The invention as set forth in claim 8, wherein the ratio of the intermediate frequency for a given carrier frequency band to the minimum frequency of the corresponding carrier frequency band is a constant for all carrier frequency bands.

10. In a superheterodyne receiver for the reception of signals in the desired one of a plurality of frequency bands, the combination with a carrier wave amplifier stage, of an oscillator for generating currents to beat with received signals to produce a modulated signal of intermediate frequency, said amplifier stage and oscillator each including resonant circuits having substantially identical adjustable condenser sections, and tapped inductances of different magnitudes, and means for adjusting the effective magnitudes of said inductances in accordance with the frequency band in which the desired signal lies, the sections of said inductances between the taps thereof being so related that a constant ratio of the effective inductances is maintained for all of said frequency band adjustments.

11. A superheterodyne receiver of the type adapted to be tuned over a plurality of frequency bands, and having intermediate frequency transformers adjustable to a different frequency for each band of received signals, a carrier wave circuit including a relatively fixed reactance and an adjustable reactance, an oscillator circuit including a relatively fixed reactance and an adjustable reactance substantially identical with the adjustable reactance of said carrier wave circuit, and means for adjusting the magnitudes of said fixed reactances to different values for each band of received signals, the ratio of the effective magnitudes of said relatively fixed reactances being constant for all frequency bands, whereby no alining adjustment of said adjustable tuning reactances is required to insure a constant beat frequency for each signal band when said adjustable tuning elements are simultaneously adjusted for tuning within a frequency band.

12. In a superheterodyne receiver, the combination with a carrier wave amplifier, an intermediate frequency amplifier, and an oscillator, of means adjustable to adapt said carrier wave amplifier for tuning over two different frequency bands, means for adjusting said intermediate frequency amplifier to a constant but different frequency for each of said two carrier frequency bands, and means adjustable to adapt said oscillator for tuning over a different frequency band for each of said two different carrier frequency bands.

PAUL O. FARNHAM.

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